The present invention has particular application to bicycles referred to as mountain bikes or trail bikes (and optionally to motorcycles commonly referred to as dirt bikes) which are typically ridden over rough terrain and/or on steep uphill or downhill slopes. Although the description of the invention herein will be directed to bicycles, application of the invention to motorcycles is also known.
As is typical for all conventional bicycles, the front wheel is the steering wheel, that is, it controls the steering of the bicycle. The conventional apparatus used to perform this steering is as follows. First, steering handles, or handlebars, are interconnected to the wheel through a fork. The fork typically has parallel legs that extend upward from each side of the wheel axle and connect at the top of the wheel to a central steering tube which is, in turn, attached to the handlebars. The central steering tube is rotatably mounted to the frame of the bicycle in a manner that supports the frame on the wheel=s axle while permitting rotation of the central steering tube and thus allowing the front wheel to turn relative to the frame of the bicycle.
Additionally, it is conventional in the bicycle industry to use "quick-release" mounting devices or hubs for attaching the front wheel to the end piece of each leg of the bicycle front fork. Such end pieces are commonly referred to as dropouts. The use of these quick-release mounts is commonly used in bicycles because they facilitate removal of the wheel for repair, transport, storage, anti-theft, etc. In certain embodiments, these dropouts may also comprise mounts for attaching a conventional disc brake assembly.
Further, of particular concern to the "off-road" bicycle rider is the jolting of the front wheel as disturbances in the ground surface, such as rocks, holes, or vertical drops, are encountered. This jolting is transferred to the rider through the wheel, fork, steering tube, steering handles, and ultimately the rider=s arms. In addition to the potential discomfort to the rider, there is the added concern for safety. That is, the steering handles become difficult to control at the instant of a severe jolt being experienced by the rider through the handles.
To overcome this problem of severe jolting, designers of trail and mountain bikes have developed front wheel, shock absorbing suspension systems. These shock absorbing systems have fork legs that include stanchion tube(s) (or inner sliding tube(s)) which is connected to a fork crown for attachment to the steering assembly and thus the bicycle frame, and which is(are) slidable within rigid sleeve(s) (or outer tube(s)), while maintaining a lateral seal to prevent any liquid from leaking from the chamber within the suspension fork. In addition, these suspension forks comprise biasing member(s) which operate pneumatically, hydraulically, elastomerically or with metallic coil springs, positioned within the stanchion tube(s) and rigid sleeve(s) to achieve the "shock-absorbing" suspension action. Typically, the biasing member(s) are firmly secured to the top end of the stanchion tube(s) and the bottom end of the rigid sleeve(s).
As obstacles are encountered by the front wheel, the stanchion tube(s) slide within the rigid sleeve(s) as the biasing member(s) compress, thereby absorbing the severe jolt. Optionally, the stanchion tube(s) may be slightly tapered and may have a slight degree of rotatability within the rigid sleeve(s). Moreover, for optimal performance, the fork legs should be aligned such that when an obstacle is encountered directly the resulting upward force(s) should be in substantially the same axis as is the fork legs, such that the slidable stanchion tubes, if more than one, are displaced uniformly.
However, during cornering or other maneuvering, the forces are not in the same axis as the suspension such that torsional and lateral stresses are created, and typically one of the rods is compressed or displaced into the corresponding sleeve more so than the opposite rod. Because the slidable rod has a slight degree of rotatability within the sleeve, high stresses are created at the dropout-to-axle connection when lateral and torsional forces are applied to the wheel in contact with the ground, such as in cornering. Further, while braking in order to stop or corner, outward forces from the brakes create a large amount of torsion on the rigid sleeve(s). The resistance to this torsion is mainly provided by the wheel axle and the brake arch, if any. Thus, increased rigidity and strength are highly desired throughout the front fork, especially at the wheel axle, brake arch and/or crown regions.
One new design to increase the strength and rigidity at the wheel axle comprises an enlarged wheel hub and axle (the axle being approximately 20 mm in diameter) combined with a quick release fastening system. With a front fork suspension system the stresses are much higher than in rigid forks and therefore require increased strength and stability throughout. While uniform compressions relieve stress on the wheel, fork, steering tube, and steering handle, unbalanced compressions, such as from cornering and maneuvering, the stresses on the wheel axle remain high. Therefore, increased rigidity and strength in the wheel axle is highly desirable for off-road bicycles and motorcycles, particularly those with front suspensions. Such a novel design in discussed in co-pending application serial no. 09/189,448, which is herein incorporated by reference.
An additional concern for bicycle riders is the weight of the bicycle. A lighter bicycle is more desirable because it takes less exertion on the part of the rider to power and maneuver. As such, manufacturers of high-end performance bicycles and bicycle components are continuously upgrading their bicycles and components to decrease the overall weight of the bicycle. This has typically been accomplished in at least three ways. One is to use lighter materials such as aluminum alloys and carbon-graphite components. Another is to decrease the overall number of components that comprise a bicycle. Yet another is to decrease the thickness of the components used without sacrificing their strength.
Consequently, separate components could be combined at the front fork suspension system of the bicycle. A typical front fork suspension system includes a crown which allows attachment of the central steering tube and a pair of parallel rigid rods which are slidable in a corresponding pair of rigid sleeves. Typically, the crown has a slit on each of the outer ends which receive the parallel rigid rods and a screw or other threaded fastening device (or pair of screws or threaded fastening devices) is (are) used to tighten the opening by being received on the inner portions of the crown. The dropouts are attached or manufactured at the lower portion of the rigid sleeves. A brake arch is mounted on the lower portion of the rigid rods, typically via screws or other threaded fastening devices, one on each rod, and the brake arch has receptacles for mounting brake calipers.
An alternative design, known as an upside down (or inverted) fork, comprises rigid sleeve(s) (or outer tube(s)) attached to the crown, or mad as a part of the crown, in which corresponding stanchion tube(s) (or inner sliding tube(s)) slide. Accordingly, the dropout(s) is(are) attached or manufactured at the lower portion of the stanchion tube(s), while the brake arch, if any, is mounted on the upper portion of the stanchion tube(s). On conventional inverted fork designs, the crown is typically mounted to the rigid sleeves in the same fashion as it is mounted to the stanchion tube(s) in the non-inverted fork designs.
Recent trends show an increased use of disc brakes on motorcycles and bicycles due to their increased performance and high durability. Typical disc brake systems are mounted on one of the dropouts at the wheel axle for maximum performance. Conventionally, the disc brakes comprise a separately mounted caliper containing the brake pads which, when in the closed position (i.e., pressed together), provide a high degree of frictional force to slow the wheel to a stop. It is therefore appreciated that the present invention can be used with bicycles or motorcycles having either a conventional brake arch design or a conventional disc brake system.
With the increased popularity of mountain biking, and the desire to attack a variety of terrains with a single bike, there has and continues to be a strong desire and need for better suspension forks which have adaptable or adjustable compression. There is especially the need for such adjustability to have the simplicity needed by the casual rider while providing the stability and precision required by the professional rider. As will be shown in greater detail in the drawings and description below, the adjustable compression suspension fork of the present invention provides just that.